The present invention relates to a material testing machine devised so as to make a test piece imposed with a test load with a crosshead driven by means of rotating screw columns
A conventional material testing machine of this kind is exemplified by FIGS. 4 and 5, which respectively show an entire frontal outlined view of the machine and a partial detailed view illustrating the construction of the left half portion of the machine. The right half of the machine, though not shown, has a symmetrically similar construction.
A pair of supporting columns 1 (FIG. 5) vertically kept on the floor holds at the lower portion both ends of a table 2 (base rack) and supports at the upper portion a crossyoke 3 horizontally. On the table is installed a pair of right and left screw columns 4, by which a crosshead has both its ends supported through a pair of corresponding screw nuts (not shown). Each of the screw columns 4 has its lower end connected with a reduction gear 6 driven by a not shown motor through a rotation shaft 7.
The upper side of the table 2 and the lower side of the crosshead 5 are respectively provided with facing clutches (not shown) forming a pair of material gripping tools. Rotation of the motor in a predetermined direction, with a test piece gripped on both the ends by the clutches, makes each of the screw columns 4 to rotate through the rotation shaft 7 and the reduction gear 6, causing the crosshead 7 screw-engaged with the screw columns 4 to rise upward. The upper clutch fixed to the crosshead 5 is then lifted up to exert a tensile force to the test piece. Further, a reference numeral 8 in FIGS. 4 and 5 stands for a cover protecting the supporting columns 1 and the screw columns 4.
In such a general constitution of the machine, a longer test piece necessitates, as a matter of course, a larger distance between the crosshead 5 and the table 2. This requirement has conventionally been coped with replacement of the screw columns 4 with longer ones, whose cost is generally increased with an increase in length. However, if the elongation due to a tensile force is small, even a long test piece caused the stroke of the crosshead in operation to ramain short. This means that only a short region of the long screw columns is used in practice. Therefore, it is uneconomical to use expensive long-sized screw columns.